/Engine/Plugins/FX/Niagara/Source/NiagaraShader/Public/NiagaraShared.h
Save "stable" shader for identifying the shader in the recorded PSO cache.
void SaveShaderStableKeys ( EShaderPlatform TargetShaderPlatform, struct [FStableShaderKeyAndValue](API\Runtime\RenderCore\FStableShaderKeyAndValue) & SaveKeyVal )